1. Technical Field
The present invention refers generally to an access apparatus and the method thereof. More specifically, the present invention relates to a gateway proxy apparatus and method for connecting legacy Public Switch Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) terminal users to a IP Multimedia Subsystem (IMS) system in the telecommunication area.
2. Background Discussion
IMS (IP Multimedia Subsystem) system architecture is proposed by 3GPP (the 3rd Generation Partnership Project) organization. It is based on soft switching technology and is a subsystem that is super positioned on GPRS (General Packer Radio Service) network for supporting IP multimedia service. The main feature of IMS is that it employs SIP protocol (Session Initiation Protocol) as call control protocol and based on this, it realizes the irrelativeness between the service and the access network.
However, although IMS can realize the irrelativeness between the service and the access network, the access of legacy PSTN/ISDN terminal is not supported in conventional architecture.
Typically, integrating legacy fixed terminal service, a PSTN/ISDN emulation subsystem is usually super positioned on the basis of current IMS subsystem architecture, two methods are usually employed: one is that the legacy terminal connects to the gateway, and visits I/S-CSCF (Interrogating/Servicing CSCF) through P-CSCF using the gateway, and then the application layer provides PSTN/ISDN emulation service control; the other method is that AGCF (Access Gateway Control Function) is employed, wherein the legacy terminal connects to the gateway, controlled by AGCF, and visits I/S-CSCF through AGCF by gateway and then the application layer provides PSTN/ISDN emulation service control. Both the access methods need PSTN/ISDN emulation service equipment to provide PSTN/ISDN service for legacy terminals.